In a scanning tunneling microscope (STM), which is a typical SPM, a surface topography of a sample is observed using a needle-like probe called "tip" whose apex is placed in the proximity of the sample surface (the gap between the apex of the tip and the surface of the sample is of the order of 1 nm=10.sup.-9 m). The tip is fixed to a tip scanning driver which moves the apex of the tip in the x, y and z directions (where z is the direction parallel to the tip) using piezoelectric actuators. A certain voltage (about .+-.0.1-3 V) is applied between the tip and the sample to cause a tunneling current to flow between them. While the tip is scanned through the x-y plane, the tunneling current is maintained constant by properly moving the tip in the z direction, whereby the surface topography is obtained. The resolution of the STM can be up to the dimension of atoms.
Conventional STMs are mainly used for observing non-biological samples such as metals, semiconductors, etc., in which case the sample is placed in a highly evacuated chamber and the surface is cleaned by heating the sample to a high temperature or a cleaved new surface is produced.